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NCERT Exemplar · Q44

Q.Give any six features of the human genome.

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The human genome—our complete DNA instruction set—contains roughly 3 billion base pairs, about 30,000 genes (far fewer than expected), and reveals that humans share 99.9% of their sequence, with most DNA surprisingly non-coding.

The Human Genome Project, completed in 2003, was one of the most ambitious scientific undertakings of the modern era. It set out to read every letter of the genetic code that makes us human—all the DNA packed into our 23 pairs of chromosomes. What researchers discovered reshaped our understanding of heredity, evolution, and what it means to be human at the molecular level.

Here are six striking features that emerged from sequencing the human genome:

1. Size and scale: approximately 3 billion base pairs

The human genome is vast. It contains roughly 3 billion (3 × 10⁹) chemical base pairs—the A-T and G-C rungs of the DNA ladder. If you were to read out one base pair per second, it would take nearly a century to finish. Yet all this information is coiled and packed into a nucleus so small it's invisible to the naked eye.

2. Far fewer genes than expected: around 30,000

Before the project, scientists predicted humans might have 80,000 to 100,000 genes. The actual count? Only about 30,000 protein-coding genes—not much more than a roundworm (around 19,000) and fewer than some plants. This was humbling. It suggested that complexity arises not just from the number of genes, but from how they are regulated, spliced, and combined.

3. Humans are 99.9% identical

Any two humans share 99.9% of their DNA sequence. All the visible diversity—skin color, height, facial features—stems from variations in just 0.1% of the genome. This underscores our fundamental biological unity as a species and dismantles any genetic basis for race as a biological category.

Note

That 0.1% difference amounts to about 3 million base pairs—still a substantial number of variations (called SNPs, or single nucleotide polymorphisms) that contribute to individual uniqueness and disease susceptibility.

4. Most of the genome does not code for proteins

Less than 2% of the human genome actually consists of genes that code for proteins. The rest was once dismissed as "junk DNA," but we now know much of it has regulatory functions—controlling when and where genes are turned on or off, or playing structural roles in chromosomes. Some stretches are indeed evolutionary relics, but the non-coding majority is far from useless.

5. Repetitive sequences and "jumping genes" …

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